1. Field of the Invention
This invention relates to a method for making a semiconductor light emitting device, more particularly to a method involving the formation and removal of buttresses and a base layer from a first supporting substrate so as to transfer a light-emitting structure from the first supporting substrate to a second supporting substrate.
2. Description of the Related Art
Since SiC or sapphire has a lattice constant similar to gallium nitride-based material, conventional gallium nitride-based light emitting diodes normally use silicon nitride (SiC) or sapphire (α-Al2O3) as a substrate for deposition of a gallium nitride-based light emitting layer thereon. However, since SiC can absorb light, the light extraction efficiency of the conventional light emitting diodes is considerably reduced when SiC is used as the substrate. In addition, since sapphire has a refractive index smaller than that of nitride-based compound and greater than that of air, total internal reflection can occur within the light emitting diode when sapphire is used as the substrate. This has an adverse effect on the light extraction efficiency.
FIG. 1 illustrates how a conventional gallium nitride-based light emitting diode is formed. The conventional light emitting diode is formed by depositing a lift-off layer 12 on a first supporting substrate 11 that is made from SiC, a multi-layered light-emitting structure 13 on the lift-off layer 12, and a metal reflective layer 14 on the light-emitting structure 13, attaching a second supporting substrate 16, which is made from Si, to the metal reflective layer 14 through an adhesive 15, and subsequently separating the light-emitting structure 13 from the first supporting substrate 11 (see FIG. 2) by applying a laser beam to the lift-off layer 12. First and second electrodes 181, 182 are formed respectively on the second supporting substrate 16 and a cladding layer 131 of the light-emitting structure 13.
By transferring the light-emitting structure 13 from the first supporting substrate 11, which is made from SiC or sapphire, to the second supporting substrate 16, which is made from Si, the aforesaid drawback regarding reduction of light extraction efficiency can be overcome. In addition, the removed first supporting substrate 11 can be reused. However, by virtue of the structure of the lift-off layer 12, removal of the lift-off layer 12 using a laser beam is difficult and may result in damage to the light-emitting structure 13, thereby adversely effecting the production yield of the light emitting diode.